BCG Potential Test

Hey guys,
I am taking the BCG potential Test in a few days in Paris and I wanted to get a feedback from people who already took it. Is it harder than the McKinsey PST? How would you guys advise to prepare?
Besides, the email from the HR tells me that I will be allowed to use a calculator but I find many comments from people telling that they were not allowed to use one. An explanation?
Cheers

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